The aim of this study was to evaluate the dentofacial effects of a modified tandem traction bow appliance (modified TTBA) in skeletal Class III subjects, and the effect of age on treatment response. The material consisted of the pre-treatment/pre-observation and post-treatment/post-observation lateral cephalograms and hand-wrist films of 45 children with skeletal and dental Class III malocclusions. Thirty patients were treated with a modified TTBA. Two treatment groups of 15 patients each were formed: an early (nine girls, six boys; mean skeletal age: 8.18 ± 0.50 years) and a late treatment (5 girls, 10 boys; mean skeletal age: 11.75 ± 1.00 years) group. The remaining 15 children (5 girls, 10 boys; mean skeletal age: 7.90 ± 0.62 years) were observed without treatment for 8 months and served as a control for the early treatment group. Wilcoxon and Mann-Whitney U-tests were used for statistical analysis. Significant forward maxillary movement was determined in both treatment groups (P < 0.01) while the decrease in SNB was significantly greater in the early treatment group compared with the control (P < 0.01). Upper molar tipping and sagittal displacement of point A (point A-T, N(⊥)FH-A) was found to be significantly greater in the late treatment group compared with the early treatment group (P < 0.05). In both treatment groups, dental and skeletal correction of the Class III malocclusion was achieved.